CW execs revealed the final storyline to UsMagazine.com. It will revolve around an unstable Serena van der Woodsen, the New York socialite played by Lively: "Serena has gone off the grid, beyond even the reach of Gossip Girl. Her friends fear for the worst and hope for the best, but even they can't imagine where they will ultimately find her."

"Gossip Girl" will air on Mondays at 9-10 p.m. and will be replaced by the "Sex And The City" prequel series "The Carrie Diaries" in January.